Walking through Win32/Jabberbot.A

Malware authors have a solid track record in regards to creative Command and Control protocols. We’ve seen peer-to-peer protocols, some custom (Sality), some standard (Win32/Storm uses the eDonkey P2P protocol). We’ve seen binary protocols (Win32/Peerfrag, aka Palevo). We’ve seen other custom protocols that leverage other standard protocols such as HTTP (Win32/Georbot), DNS (Morto)and IRC (Win32/AutoRun.IRCBot.AK), and others that leverage popular web services such as Twitter (OSX/Flashback).

We have seen malware using XMPP before as a mean of data exfiltration (RSA FraudActon Research Labs wrote extensively about one such example at Zeus Trojan Leverages IM Software to Forward Stolen Online Account Data). However, this infection is different in that the entire Command-and-Control (C&C) infrastructure relies on the XMPP protocol and a free, public Jabber server for communications.

While this threat is not new (Dr. Web has a short analysis in their virus encyclopedia here). ESET decided to publish this analysis since it presents a naive implementation that could otherwise be much more reliable and robust.

Infection scale, installation and persistence

We do not know the exact propagation vector of this threat. Our telemetry data shows that the infection scale is small but heavily concentrated in Ukraine.

Once executed, Win32/JabberBot.A copies itself into the %windir%system32 directory with a pseudorandom filename and adds an entry in the Windows registry at [HKLMSOFTWAREMicrosoftWindowsCurrentVersionRun] in order to start itself whenever a user logs in to the system.

The malware will also try to infect any removable device by copying itself to the root of the device using a hardcoded filename. While it looked like a random string at first glance, the intrepid eye can distinguish a pattern in it.

If you tokenize it this way: “luxa eterna by taenarong […]” and search on that, it leads to the following web page:

Figure 1. Search result for a hardcoded filename.

Hard to tell the reason this was chosen, your guess is as good as mine.

It is also worth noting that no AUTORUN.INF file is created on the removable device, making this propagation technique poor to say the least.

C&C protocol: leveraging XMPP

To understand how the XMPP protocol is used by this threat, we need to explore some under-the-hood details of the protocol. This Wikipedia article for XMPP explains the JabberID (JID) Resource element, which is the key to communication with the C&C.

In order to use Jabber instant messaging, you first need a user account on a given server, which starts with the format of an email address: <username>@<jabber server>. XMPP, however, allows users to log in multiple times simultaneously using the same JID, provided that the client specifies a different Resource identifier. This extended JID looks like <username>@<jabber server>/<resource>.

In the case of Win32/JabberBot.A, a common user account is shared by all the infected hosts is trednet@jabber.ru. Each instance of the bot will generates a pseudorandom resource identifier.

The botmaster most likely controls a master Jabber account on jabber.ru and has the user trednet@jabber.ru in its contact list. The XMPP protocol allows the botmaster to access to the list of resources available from another contact, which allows the botmaster to communicate with individual bots.

Figure 2. Bots announcing their presence status.

The communication protocol uses in-band XMPP messaging, with no encryption or authentication being used, even though Transport Layer Security (TLS) is supported by both the XMPP protocol and the jabber.ru service.

The malware has the basic trojan horse commands:

delete | del | dlt

Delete a local file

shell | shl

Open a local file – ShellExecuteW(“open”, <filepath> )

system | sys

Execute a system command – system(<command>)

visit | vst

Visit a given URL – ShellExecuteW(<url>)

build | bld

Upload a local file to the botmaster (in-band base64 messages)

download | dwl

Download remote a file from the botmaster (in-band base64 messages)

ping | png

Get information about the bot (platform’s username and network hostname)

cd | dir

List content of local directories

exit

Make the bot’s executable quit (no uninstallation is done, the bot will restart with a new user login)

For some reason, the author created shortened versions of each command, maybe for some sort of backward compatibility or to save some electrons.

The Upload and Download commands involve file transfers between both Jabber accounts: the transfers are done in-band of the XMPP text messaging protocol, in 4,000 bytes chunks of text encoded as base64 data. It does not use out-of-band binary transfers, most likely to avoid firewall and network address translation (NAT) issues.

Conclusion

This threat does not make use of binary packing to encrypt its files, nor does it perform any obfuscation or encryption of its network traffic. It relies on just two Jabber accounts on a free, low-profile Jabber service, which leaves it easily vulnerable to a full and complete takedown, given a minimal level of cooperation from jabber.ru. The Jabber protocol implementation used by the bot is also custom-written, where freely available libraries could have been used, instead.

All these details lead us to the conclusion that this threat is not sophisticated at all. Some of my colleagues even suggested that this was merely a school exercise. Maybe it was just that.

Nonetheless, it shows that XMPP can be used for reliable C&C infrastructure if a proper design was implemented.

At time of analysis, the botnet seemed abandoned as less than 10 bots were observed. ESET still contacted the administrators of the Jabber server at jabber.ru, who took rapid action in taking down the accounts involved in this operation. We consider the C&C eradicated.

Big hat tip to Benjamin Vanheuverzwijn for the entire technical analysis of this threat.